Internal combustion engines produce exhaust gases containing a variety of pollutants, including hydrocarbons (HCs), carbon monoxide (CO), and nitrogen oxides (“NOx”). Emission control systems, including exhaust gas catalysts, are widely utilized to reduce the amount of these pollutants emitted to atmosphere. A commonly used catalyst for gasoline engine applications is the “three-way catalyst” (TWC). TWCs perform three main functions: (1) oxidation of carbon monoxide (CO); (2) oxidation of unburnt hydrocarbons; and (3) reduction of NOx to N2.
TWCs, like other exhaust gas catalysts, typically achieve very high efficiencies once they reach their light-off temperature. TWCs that have a low light-off temperature allow the catalyst to work sooner by decreasing the time it takes for the exhaust system to reach the temperature required for operation. Because exhaust gas is untreated before reaching light-off, this period can lead to increased emissions. As even more stringent national and regional legislation lowers the amount of pollutants that can be emitted from diesel or gasoline engines, reducing emissions during the period of time before light-off is becoming a major challenge. Thus, methods and new catalysts for reducing the level of NOx and hydrocarbons emitted during cold start condition continue to be explored.
As with any automotive system and process, it is desirable to attain still further improvements in exhaust gas treatment systems, particularly under low temperature conditions. We have discovered a new three-way catalyst that provides enhanced cleaning of the exhaust gases from internal combustion engines.